1. Field of the Invention
The present invention relates to an imaging device installed on a movable body which autonomously controls motion thereof based on obtained images, and in particular, the present invention relates to an imaging device for an autonomously movable body which can autonomously calibrate the imaging device, to a calibration method for the imaging device, and to a calibration program for the imaging device.
2. Description of the Related Art
A movable robot has been known in the art, which takes images of the surrounding environment using a camera, determines a moving path for itself while detecting objects and obstacles in the surroundings by processing the obtained images, and autonomously moves along the determined moving path.
When the surrounding images are taken by a camera, the resulting images are often affected by ambient light. In general, an artificial lighting emits light which is different from sunlight, for example, a fluorescent lamp emits more green light than other colors of light, and an incandescent lamp emits more orange light than other colors of light. When images are taken under such artificial lighting, the obtained images may look different from the actual appearance of the objects in terms of color, i.e., the images may exhibit a slight additional color. In order to prevent such phenomenon, a white balance adjustment as a measure for color correction has been known. In general, cameras are classified by the type for performing white balance adjustment, i.e., there are a camera in which the white balance adjustment is fixed, a camera in which the white balance adjustment is automatically performed, and a camera in which the white balance adjustment is manually performed; however, in the case of a camera having a function of automatic white balance adjustment, the automatic color correction may be too excessively performed to create images having realistic colors. On the other hand, in the case of a camera having a function of manual white balance adjustment, the white balance adjustment may be freely adjustable.
Because an autonomously movable robot must move anywhere regardless of night and day, the influence of changes in ambient light must be minimized in order to improve accuracy of environment perception while using a camera of the type of visible light; therefore, a problem is encountered in that a white balance adjustment must be performed whenever the ambient light conditions change.
A further problem is encountered in that it is difficult for the operator to determine a timing at which the white balance adjustment must be performed.
A camera or an imaging device for solving the above problems is disclosed, for example, in Japanese Unexamined Patent Application, First Publication No. Hei 06-121321 (specifically, in FIGS. 2 and 3 thereof). In order to preferably perform a white balance adjustment without being influenced by the colors of a subject's clothing, an indoor wall, or the like, the imaging device is provided with a semitransparent lens cover, which is electrically opened or closed, in front of the lens thereof for taking images. The imaging device, first, takes images through the semitransparent lens cover when power is turned on or a command is input from outside, and takes further images after performing color correction and opening the semitransparent lens cover.
An electronic camera is also known from Japanese Unexamined Patent Application, First Publication No. Hei 10-4558 (specifically, in FIG. 1 thereof), which converts color tone under lighting for image taking into color tone under daylight, and which outputs images having color tone adjusted to the chromatic adaptation of human eyes.
However, because the imaging device disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 06-121321 performs a white balance adjustment using the ambient light passed through the clouded semitransparent lens cover, the result of the white balance adjustment is determined by the chromatic transmission characteristics of the lens cover; therefore, the ambient light affects the result to some extent. Moreover, because the white balance adjustment is performed using transmitted light, the white balance adjustment is not necessarily performed under the same conditions as for practical environment perception. In other words, a problem is encountered in that an appropriate color correction cannot be performed by using the light transmitted through the lens cover because the ambient light reflected by objects must be taken as images for an autonomously movable robot to perceive the surrounding environment.
On the other hand, in the case of the electronic camera disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 10-4558, because a white balance adjustment is performed so that the obtained images are naturally seen by human eyes, the resulting color correction may not be suitable for an autonomously movable robot to perceive the surrounding environment. When the autonomously movable robot perceives the surrounding environment, it is more important to maintain the perception results of the objects to be constant without having influence of the ambient light than to make the objects be naturally seen in terms of colors; therefore, a problem is encountered in that a white balance adjustment which is performed so that the obtained images are naturally seen by human eyes does not necessarily result in color correction which is suitable for surrounding environment perception.